This invention relates to a method for reclaiming used hydraulic fluid. More particularly, this invention relates to a method for reconstituting contaminated, petroleum base hydraulic fluids to a form and quality that permits their re-use in applications which previously required the use of new hydraulic fluids.
The utilization of hydraulic fluids for various aerospace applications requires the use of fluids that meet stringent quality specifications. Generally, the servicing of aircraft landing gear and control systems with hydraulic fluids necessitates strict compliance with quality specifications. Consequently, the used fluids must be constantly replaced with new fluids resulting in increased operating costs. In an attempt to obviate this problem, considerable research has been conducted in an attempt to develop methods of reconstituting the used fluid for use in the same manner as a new fluid. The conventional prior art methods, however, employed either a distillation technique or a diatomaceous earth filtration technique. In either case, the technigue removed the various additive ingredients which formed an integral part of the hydraulic fluid. After reconstituation with these prior art methods, the expensive additive materials, such as oxidation inhibitors, corrosion inhibitors and antiwear agents, had to be completely replaced which tended to counteract any economic savings resulting from the use of a reconstituted product.
With the present invention, however, a method for reclaiming hydraulic fluids has been found that does not require the complete replacement of all additive materials, but allows for the mere supplementation of such additives. The filtration and reconstitution is accomplished without the use of distillation or diatomaceous earth filtration. The method involves a four step process which treats used hydraulic fluids containing particulate matter, water and freon gas contaminants. The process has proven to be especially effective in reclaiming used petroleum base, hydraulic fluids which meet the Military Specification requirements of MIL-H-5606C and MIL-H-6083 D, thereby rendering them reuseable for various aerospace applications such as aircraft landing gear and control systems.